The present invention relates to a processing method and a processing device of conditioning an electron gun to improve the withstand voltage property thereof by removing a factor of discharge existing on a surface of an electrode or an insulator forming the electron gun.
As shown in a schematic cross-sectional view of FIG. 6, an electron gun 100 used, for example, for an electron beam drawing device is disposed above an electron optical body tube 101, and is provided with a pair of first electrodes 102 (102a, 102b), a second electrode 102, and a third electrode 104 (e.g., a Wehnelt electrode).
Here, in the operation of the electron beam drawing device, the inside of the electron beam 100 and the electron optical body tube 101 is maintained in a high vacuum condition (e.g., about 10−7 Pa), and a high voltage of about 50 kV, for example, is applied between a cathode 105 attached on the tips of the first electrodes 102 and the third electrode 104 (an anode). Then, a thermion is emitted form the cathode 105 made of lanthanum hexaboride (LaB6) in accordance with a voltage (not shown) applied between the first electrodes 102a and 102b, and accelerated by the high voltage described above to be discharged as an electron beam 106 inside the electron optical body tube 110. The electron beam 106 is shaped to have a desired shape by various kinds of lenses, various kinds of deflectors, a beam shaping aperture, and so on (not shown) disposed inside the electron optical body tube 101 to be used for drawing.
In the electron gun 100 described above, the third electrode 104 is connected to a negative pole side of a high voltage source 108 via an extraction electrode 107 and the first electrodes 102 are connected to the negative pole side of the high voltage source 108 described above via a bias power source 109. Thus, the third electrode 104 becomes, for example, about 500V higher than the first electrodes 102 in the negative pole direction. Further, the second electrode 103 is connected to a positive pole side of the high voltage source 108 to be kept at the ground potential. Here, although not shown in the drawings, the first electrodes 102a, 102b, the second electrode 103, and the third electrode 104 made, for example, of stainless steel are separated to be isolated with, for example, ceramics insulators.
When the high voltage is applied to such an electron gun 100 as described above, abnormal discharge caused by a discharge factor such as a protruding section like a burr or a scratch, or an attachment like dust on the surface of the electrode occurs among the electrodes, particularly between the second electrode 103 and the third electrode 104 in some cases. In other cases, massive creeping discharge caused by a discharge factor such as an impurity or attachment on the surface of the insulator between the electrodes occurs. The frequency of such abnormal discharge is high in the initial stage of several tens of hours from the commencement of use of an electron gun after attaching the new electron gun, replacing the electron gun, or maintenance of the electron gun.
The generation of the abnormal discharge cases, for example, voltage drop of about 500V in the operation of the high voltage source 108 of the electron beam drawing device to stop the operation thereof. Further, the electron bean originally required in an electron beam drawing process disappears to cause the production yield to be lowered by deterioration of the drawing accuracy, and to cause the operation rate of the drawing device to be lowered by stopping the operation of the drawing device.
Therefore, in order for suppressing or preventing such generation of the abnormal discharge, it is generally performed to execute a conditioning process (also referred to as a knocking process) of the electron gun after attaching or replacing with a new electron gun or after the maintenance of the electron gun (see, JP-A-2005-026112).
The conditioning process performed generally will be explained with reference to FIGS. 6 and 7. FIG. 7 is a graph showing an example of a waveform of a voltage applied to the electrodes of the electron gun in the conditioning process in the related art. In the conditioning process of the electron gun 100 shown in FIG. 6, for example, the inside of the electron optical body tube 101 and the electron gun 100 communicated therewith is evacuated to be high vacuum (e.g., 10−5 Pa) by a vacuum exhaust device (not shown) disposed below the electron optical body tube 101. Then, the voltage application between the first electrodes 102a and 102b is stopped to keep the emission of a thermion from the cathode 105 stopped, and the negative voltage of the high voltage source 108 is applied to the first electrodes 102 via the bias power source 109, and directly to the third electrode 104. Further, the second electrode 103 is fixed to the ground potential.
In this case, the absolute value of the negative voltage of the high-voltage source 108 is gradually increased from a low application voltage to a high voltage stepwise at constant time intervals as time passes as shown in FIG. 7. For example, the application voltage is increased in the condition of rising by 1 kV through 5 kV in one minute interval, thus performing the conditioning process of the electron gun 100. Then, the highest value of the application voltage is set, for example, to about 1.6 times of 50 kV, which is an actual working voltage of the electron gun, namely 80 kV, and the voltage of the highest value is held for a predetermined period, for example, about 10 minutes while confirming that no abnormal discharge occurs, and then the conditioning process is terminated. If the abnormal discharge occurs in the termination judgment of the conditioning process, the voltage is lowered to a predetermined value and the conditioning process is performed again from the lowered voltage, and is repeated until the abnormal discharge described above stops occurring.
By executing such a conditioning process, namely electrode spark erosion, on the electron gun, the discharge factors described above on the surfaces of the first electrodes 102, the second electrode 103, the third electrode 104, and the insulators described above are eliminated, thus the withstand voltage property of the electron gun is improved.
However, in the past conditioning process of the electron gun, there are some cases in which massive discharge occurs at a high frequency in the conditioning process, the discharge causing damages such as roughening or cracks on the surfaces of the electrodes or the insulators of the electron gun. For example, the massive discharge makes a crater-shaped breakage on the surface of the electrode, and the small fragment adheres to another place and remains there. Therefore, the life of the electron gun is problematically shortened.
Further, it has been proved that if the microscopic protrusion, impurity, and attachment causing the microscopic discharge is not sufficiently removed in the conditioning process, the abnormal discharge caused by the factor of the microscopic discharge described above is apt to occur in the actual use of the electron gun. Further, it has been proved that in the past conditioning processing method, the factors of the microscopic discharge including the fragment described above cannot sufficiently be removed, and accordingly there is a limitation in improvement of the withstand voltage property of the electron gun.
Such a problem occurs not only in the case with the electron gun implemented in the electron bean drawing device described above, but also in the case with electron guns to be other electron sources for emitting electrons by high electric fields as well.